Abstract

Experiments have shown that for thixotropic sol-gel systems consisting of ZnFe₂O₄ nanoparticles without any matrix material, the measured magnetization, or susceptibility of gels, are greater than those of sols. For the reduced susceptibility, a system with a volume fraction of particles of f_v=2.0% is lower than a system with f_v=1.5%. These results have been interpreted in terms of a magnetization mechanism based on the Brownian rotation of the moments fixed inside the colloidal particles, which would be dramatically affected by the non-magnetic hydrodynamic interaction. For weakly cross-linked gels, the translational degree of freedom is “frozen” while the rotational degree of freedom remains unchanged, so that their hydrodynamic interaction effect is weaker, and they are more easily magnetized than the sols with both rotational and translational degrees of freedom. The action of gelation preventing the hydrodynamic interaction effect on the magnetization process can be referred to as the “gelation decoupling”. Correspondingly, such behavior of the hydrodynamic interaction in affecting the apparent magnetism can be referred to as a “viscomagnetic effect”.

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